Test apparatus and a method of testing of an antenna

ABSTRACT

The present invention teaches a measurement apparatus for the measurement of a test antenna comprising: a movable stand for supporting the test antenna, a feed antenna having a plurality of radiating elements. The movable stand is located at a predefined distance from the feed antenna. An antenna feed system is provided with a plurality of adjustment components for adjusting the phase and amplitude of a wave front from the plurality of radiating elements such that at the distance the wave front is substantially planar.

FIELD OF THE INVENTION

The disclosure relates to a test apparatus for the testing of an antennaand a method for the testing of an antenna in the test apparatus.

BACKGROUND TO THE INVENTION

There are a number of methods known for the measurement of a radiationpattern and for testing of antennas for mobile communications.

Far-field measurements of the antenna being tested can also be carriedout in the open air. These measurements, however, require the distancebetween the antenna being tested and the detector to be at a significantdistance to eliminate near-field effects. For example, the measurementof a mobile communication antenna having a length of 2.6 m at 1 GHzrequires the detector to be at a distance of 45 m from the antenna beingtested. The measurements in the open air are affected by reflectionsfrom nearby bodies and also possibly interference from other mobilecommunication antennas operating at neighbouring frequencies.

It is possible to use a shielded measurement anechoic chamber in orderto measure the near-field radiation pattern of the antenna and thencalculate the far-field radiation pattern. These measurement chambers donot require as much space as far-field measurements. The measurementchamber can be, for example, around 10 m in size. The value of the fieldas well as the phase is measured over the solid angle surrounding theantenna (or at least a substantial part of the solid field) and it isthen possible to calculate the far-field radiation pattern of theantenna being tested from this receiving pattern. This calculationrequires knowledge of the phase of the radiation being measured, whichis generally available for passive antennas. However, knowledge of thephase is generally not available for active antennas. These measurementscan also require a significant amount of time to perform.

A further apparatus for measuring the radiation pattern of the testantenna is a so-called compact range chamber. The compact range chamberuses the spherical field from a feed antenna and directs the field usingone or more curved mirrors in order to create a far-field withsubstantially parallel wave fronts at the test antenna. The test antennais placed in this far-field in the so-called quiet zone where the wavefront is substantially planar. The compact range chamber enables thedirect measurement of the far-field but requires a measurement chamberthat is larger than that for measuring a near-field. This is because thecurved mirrors used in the measurement chamber require a dimension thatis at least twice as large as the test antenna. For example, a 2.6 mmobile communications antenna requires a curved mirror having around 5 mdiameter. Such a compact range chamber has the further disadvantage thatthe direct beam between the feed antenna and the test antenna candisturb the measurements. It would be possible to build a compact rangechamber that produces a cylindrical wave in the measurement zone. Thesecompact range chambers are, however, substantially more difficult toconstruct. It would also be possible to use lenses instead of curvedmirrors to produce the far-field.

FIG. 1 shows an arrangement for testing a test antenna 2 according tothe prior art. A feed antenna 4 is oriented towards a reflector 3, theshape of which is designed to reflect the spherical wave in anapproximately planar manner. FIG. 2 shows an example of an antenna 20under test of which the radiation pattern is to be measured. The antenna20 is mounted in a so-called quiet zone of an anechoic test apparatus 10on a measurement stand 30, which comprises a rotatable horizontal axis34 to which the antenna 20 is attached by struts 36. The antenna 20 canbe rotated 360° about the horizontal axis 34, as indicated by thearrows. This enables the antenna 20 to be tested in all directions. Themeasurement stand 30 is further connected to a vertical axis 32 toenable the measurement stand 30 to be rotated in a directionsubstantially perpendicular to the plane of the floor of the testapparatus 10, as indicated by the arrow. The combination of the rotationof the vertical axis 32 and the horizontal axis 34 enables the radiationpattern of the antenna 20 to be measured in all spatial directions.

A probe or detector 80 measures the radiation pattern from the antenna20. The probe 80 is connected to a measurement apparatus 90, which isable to calculate the radiation pattern from the measurements. Thedistance between the probe 80 and the antenna 20 under test is chosen tobe sufficiently large that reflections do not affect the result.

Chinese Patent Application No. 102854401 teaches a method for measuringthe radiation pattern from an antenna array under test. The methodcomprises measuring the radiation patterns of the antenna array byirradiating the antenna array from different angles by uniform planewaves. The response of the antenna array under the irradiation of theplane waves is measured by a digital oscilloscope. The responses arenormalized to obtain the radiation patterns of the antenna array underthe conditions of uniform amplitude and co-phase excitation and theradiation pattern can be calculated through digital signal processingtechnology and a superposition principle of the patterns of the arrayantenna unit.

Japanese Patent Application No. JP 2012-117959 (Mitsubishi Electric)teaches an antenna measurement method, which comprises generation of aradio frequency signal (RF) followed by changing an amplitude and aphase of the high frequency signal corresponding to an element antennato be a measured. The RF signal is sent from a plurality of antennaelements and the resulting RF signal is received at the antenna beingmeasured.

SUMMARY OF THE INVENTION

A measurement apparatus for the measurement of a test antenna isdisclosed. A feed antenna is mounted in the measurement apparatus andcomprises a plurality of radiating elements. The test antenna is placedon a moveable stand, at a predefined test distance from the feedantenna. The feed antenna is fed using an antenna feed system, having aplurality of adjustment components for adjusting the phase and amplitudeof a wave front from a plurality of radiating elements. The plurality ofadjustment components adjusts the phase and amplitude of the wave frontfrom the feed antenna such that the wave front is substantially planarat said predefined test distance.

The adjustment of the phase and amplitude of test signals from the feedantenna enables a substantially parallel wave front to be created at thepredefined test distance. In other words, a quiet zone is created at thelocation at which the radiation pattern of the test antenna is measured.This measurement apparatus does not require a mirror in order to directthe wave front such that the wave front is substantially parallel at theantenna being tested. The use of the plurality of radiation elements,which could be placed in groups, enables the wavefront to be controlled.

The test antenna is placed at the predefined test distance correspondingto the quiet zone of the feed antenna. The position of this quiet zonedepends on the phase and amplitude settings of the feed antenna and cantherefore be adjusted to different requirements, which include a size ofthe test antenna, a size of the feed antenna, a sufficient distancebetween the test antenna and the feed antenna to reduce signalscorrupted by multiple paths reflected between the test antenna and thefeed antenna, and a small distance to fit into an anechoic chamber. Thephase and amplitude settings of the feed antenna may be adjusted togenerate a large quiet zone. A non-limiting example could be, e.g. for afrequency of 1-2 GHz, a feed antenna length of 4 m, a test antennalength of 2 m, the predefined test distance between the test antenna andthe feed antenna could be a distance of 4 m. The phase and amplitudesettings can be adjusted during the design of measurement apparatus. Thephase and amplitude settings can be adjusted depending on the testantenna to be tested.

The test antenna is placed on a moveable stand, which is rotatablearound at least one axis. In a preferred embodiment the stand can berotated about two axes. One of the two axis is a substantially verticalaxis and the other one of the two axes is a substantially horizontalaxis. This allows the test antenna to be moved in three dimensions suchthat the radiation pattern from the test antenna can be measured in allof the spatial angle.

The antenna feed system has delay elements and/or attenuators connectedbetween the individual ones of the radiating elements and the feedsystem. In one aspect of the invention, the delay elements arehard-wired lengths of coaxial cable, which are cut to the requiredlength. It would be possible to replace the hard-wired delay elementswith software adjustments. The plurality of radiation elements canproduce cross-polarised beams. In one aspect of this disclosure,orthogonal polarisations are used.

The disclosure also teaches a method for the testing of a test antennain a measurement apparatus comprising: placing the test antenna at amovable stand of the measurement apparatus; adjusting at least one ofphase, delay and amplitude of a wave front from a feed antennacomprising a plurality of radiating elements, to detect a substantiallyplanar wave front at the movable stand, using a plurality of adjustmentcomponents for adjusting at least one of phase or delay; emitting a testsignal by the test antenna and receiving the test signal at the feedantenna, moving the movable stand and repeating the step of emitting andreceiving to derive a radiation or transmission pattern of the testantenna.

The disclosure also teaches a method for the testing of a test antennain a measurement apparatus comprising: placing the test antenna at amovable stand of the measurement apparatus; adjusting at least one of aphase, delay and amplitude of a plurality of radiating elements, forminga feed antenna, to produce a substantially planar wave front at themovable stand, using a plurality of adjustment components for adjustingsaid at least one of a phase, delay and amplitude; emitting a testsignal by a feed antenna and receiving the test signal by the testantenna, moving the movable stand and repeating the step of emitting andreceiving to derive a reception pattern of the test antenna.

When the test antenna is an active antenna, both the reception patternand the transmission pattern of the active antenna should be tested.

In one aspect of this disclosure, the test signal is generated with atleast two orthogonal polarisations. The two orthogonal polarisationsenable the testing of test antennas with arbitrary polarisation.

The method provides a way to measure the far-field radiation pattern ofthe antenna under test without the need to test in the open air or toconvert measurements mathematically from near-field measurements.Therefore this method can be used in a compact measurement setup forboth passive and active antennas.

DESCRIPTION OF THE FIGURES

FIG. 1 shows an example of an apparatus for measuring a test antennaaccording to the state of the art;

FIG. 2 shows an example of antenna mounted on a measurement stand in ameasurement apparatus according to FIG. 1.

FIG. 3 shows an overview of the measurement apparatus with an antennafeed system according to the present disclosure.

FIG. 4 shows an example of antenna mounted on a measurement stand in ameasurement apparatus according to fig.3

FIG. 5 shows a measurement of the power distribution of a signalgenerated by a feed antenna according to one aspect of the disclosure.

FIG. 6 shows a calculation of a power distribution across the radiatingelements in a feed antenna according to one aspect of the disclosure

FIG. 7 shows a calculation of the length of the delay elements in thefeed system according to one aspect of the disclosure.

FIG. 8 shows a method of testing a test antenna according to one aspectof the disclosure;

FIG. 9 shows a method of testing a test antenna according to yet anotheraspect of the disclosure.

DETAILED DESCRIPTION OF THE INVENTION

The invention will now be described on the basis of the drawings. Itwill be understood that the embodiments and aspects of the inventiondescribed herein are only examples and do not limit the protective scopeof the claims in any way. The invention is defined by the claims andtheir references. It will be understood that features of one aspect orembodiment of the invention can be combined with a feature of adifferent aspects or aspects and/or embodiments of the invention.

FIG. 3 shows an overview, from above, of a test apparatus 210 accordingto an aspect of the disclosure for testing a test antenna 220. FIG. 4shows an example of a test antenna 220 of which the radiation pattern isto be measured. The test apparatus 210 has a feed antenna 240 with aplurality of radiating elements 250-1, 250-2, . . . , 250-N. Theplurality of radiating elements 250-1, 250-2, . . . , 250-N is connectedto a feed system 260. The feed system 260 is connected to a test signalgenerator and receiver 262 adapted to generate and/or receive a testsignal.

The feed system 260 can be used for feeding test signal in a frequencydomain in which the test antenna 220 is to be tested. The feed system260 may further comprise two feed sub-systems for operating the feedantenna 240 in two frequency domains, e.g. in a first frequency rangebetween 700 MHz and 960 MHz and in a second frequency range between 1710MHz and 2690 MHz. This enables the use of the feed antenna 240 fortesting other test antennas in different frequency ranges.

A plurality of delay elements or phase shifters 265-1, 265-2, . . . ,265-N are present in the antenna feed system 260 which delay the testsignal received from the test signal generator 262 which is sent to thefeed antenna 240. A plurality of attenuators 267-1, 267-2, . . . , 267-Nis also present in the antenna feed system 260 which are adapted toadjust the amplitude of the radiating elements 250-1, 250-2, . . . ,250-N.

The purpose of the delay elements 265-1, 265-2, . . . , 265-N and theattenuators 267-1, 267-2, . . . , 267-N is to produce a test signal atthe radiating elements 250-1, 250-2, . . . , 250-N, which produces at apredefined test distance a planar wave front, as shown on FIG. 3. Inother words, a test signal is produced that substantially approximates afar-field pattern at the predefined test distance d without the need forthe curved mirrors of the prior art.

The plurality of radiating elements 250-1, 250-2, . . . , 250-N aredipoles having two polarisation components, such as vertical orhorizontal components, or cross-polarised components (−45°, +45°). Anypolarisation could be used. The polarisation components are orthogonalin one aspect of this disclosure.

The radiating elements 250-1, 250-2, . . . , 250-N are shown mountedlinearly in FIG. 3. It would be possible to construct a two-dimensionalarray of the radiating elements 250-1, 250-2, . . . , 250-N to produce athree dimensional field in the quiet zone.

Preferably the feed antenna 240 comprises between 15 and 30 radiatingelements (N is in the range of 15-30). It should be noted that thenumber of radiating elements depends among other on the frequency.

The delay elements 265 can be hard-wired and made, for example, from cutlengths of coaxial cable. It would also be possible to use asoftware-generated test signal without the delay elements 265 togenerate the test pattern.

FIG. 4 shows an example of a test antenna 220 of which the radiationpattern is to be measured. The antenna 220 is mounted on a measurementstand 230, at the predefined test distance d, i.e. where the wave frontis substantially planar. In other words, the measurement stand is placedin a quiet zone 215.

The measurement stand 230 comprises a rotatable horizontal axis 234 towhich the antenna 220 is attached by struts 236. The test antenna 220can be rotated 360° about the horizontal axis 234, as indicated by thearrows. This enables the test antenna 220 to be tested in alldirections. The test antenna 220 can be either an active antenna or apassive antenna.

The measurement stand 230 is further connected to a vertical axis 232 toenable the measurement stand 230 to be rotated in a directionsubstantially perpendicular to the plane of the floor of the testapparatus 210, as indicated by the arrow. The combination of therotation of the vertical axis 232 and the horizontal axis 234 enablesthe radiation pattern of the test antenna 220 to be measured in allspatial directions.

FIG. 5 shows a measurement of the power distribution signal generated bythe feed antenna 240 at the predefined test distance d, e.g. in thequiet zone, across the length of the antenna 220, which is approximately2.5 meters. It will be seen that, at a frequency of 2.35 GHz, the RFfield in the quiet zone is substantially uniform across the length ofthe antenna 220. There is a small drop-off of the power at the edges ofthe quiet zone, as might be expected.

At least ten radiating elements are needed to generate a planarwavefront at said predefined distance less than 4 meters. In one aspectof the disclosure, 15 to 30 radiating elements are provided to provide amore uniform planar wavefront, but this is not limiting of theinvention. It should be noted that the number of radiating elementsdepends among other on the frequency.

FIG. 6 shows a calculation of a power distribution across the radiatingelements in a feed antenna according to one aspect of the disclosure. Itwill be seen that the best performance of the quiet zone is achieved,when the power distribution set by the attenuators 267-1, 267-2, . . . ,267-N is almost constant in the centre of the feed antenna 240 and witha reduced power at the edges of the feed antenna 240. FIG. 7 shows acalculation of delays introduced by the delay elements 265-1, 265-2, . .. , 265-N in the antenna feed system 260. It will be seen that a delayneeds to be introduced such that the radiation of the test signal fromthe radiating elements 250-1, 250-2, . . . , 250-N, at the edges of thefeed antenna 240 is slightly delayed with respect to the test signalfrom the radiating elements 250-1, 250-2, . . . , 250-N, at the centreof the feed antenna 240. In other words, a best approximation of a planewave at the predefined test distance can be achieved with almost nodelay of the signal fed to the centre radiating elements of the feedantenna 240 and with a slight positive delay of the signal fed to theradiating elements at the edge of the feed antenna 240.

It should be noted that the phase, delay and/or amplitude of theradiating elements may be adjusted individually for each radiatingelement of the plurality of radiating elements. Alternatively, thephase, delay and/or amplitude of the radiating elements may be adjustedfor groups of radiating elements of the plurality of radiating elements,each the radiating elements of a group have the same phase, delay and/oramplitude.

Tests have shown that the results obtained from measuring the radiationpattern from the test antenna 220 in the measurement apparatus 210, asdescribed in this disclosure, are as good as those in the field andthose performed in a compact range apparatus. The far-field is used andtherefore there is no need to perform a mathematical transfoimation frommeasurement of the near-field, which would require anyway knowledge ofthe phase information of the measured data.

FIG. 8 shows a method for the testing of a test antenna in a measurementapparatus 210. The method is described with reference to the measurementapparatus 210 of FIGS. 2-3.

The test antenna 220 is placed at the movable measurement stand 230(Step S100).

The phase, delay and/or amplitude for the plurality of radiatingelements 250-1, 250-2, . . . , 250-N is adjusted to produce asubstantially planar wave front at the movable stand 230 (step S120). Itshould be noted that the adjustment of the phase, delay and/or amplitudefor the plurality of radiating elements 250-1, 250-2, . . . , 250-N maybe performed at the time of designing and manufacturing the feed antenna240. It is also possible to adjust the phase, delay and/or amplitude forthe plurality of radiating elements 250-1, 250-2, . . . , 250-Ndepending on the test antenna to be tested.

The test antenna is placed at the predefined test distance correspondingto the quiet zone of the feed antenna. The position of this quiet zonedepends on the phase and amplitude settings of the feed antenna and cantherefore be adjusted to different requirements, which include a size ofthe test antenna, a size of the feed antenna, a sufficient distancebetween the test antenna and the feed antenna to reduce signalscorrupted by multiple paths reflected between the test antenna and thefeed antenna, and a small distance to fit into an anechoic chamber. Thephase and amplitude settings of the feed antenna 240 may be adjusted togenerate a large quiet zone or a smaller quiet zone with a highintensity. For example, for a frequency in the range of 1 to 2 GHz, afeed antenna length of 4 m, a test antenna length of 2 m, the predefinedtest distance between the test antenna and the feed antenna could be adistance of 4 m.

A test signal is emitted by the feed antenna 240 and the test signal isreceived by the test antenna 220 to derive a radiation pattern of thetest antenna 220. The test antenna 220 receives a substantially planarwave front (Step S130).

The antenna 220 is rotated about the horizontal axis 234 and/or aboutthe vertical axis 232.

As noted above, the test signal is generated with at least one of twoorthogonal polarisation, for example a horizontal and a verticalpolarisation. It should be noted that the test signal could be generatedwith two non-orthogonal polarisations as well. The provision of twoorthogonal polarisations enables accurate measurements.

FIG. 9 shows another method for the testing of a test antenna in ameasurement apparatus 210. The method is described with reference to themeasurement apparatus 210 of FIGS. 2-3.

The test antenna 220 is placed at the movable measurement stand 230(Step S200).

The phase, delay and/or amplitude for the plurality of radiatingelements 250-1, 250-2, . . . , 250-N is adjusted to produce asubstantially parallel wave front at the movable stand 230 (step S220).It should be noted that the adjustment of the phase, delay and/oramplitude for the plurality of radiating elements 250-1, 250-2, . . . ,250-N may be performed at the time of designing and manufacturing thefeed antenna 240. It is also possible to adjust the phase, delay and/oramplitude for the plurality of radiating elements 250-1, 250-2, . . . ,250-N depending on the test antenna to be tested.

The test antenna 220 emits the test signal, which is received by thefeed antenna 240 working in reception or receive mode (step S230). Thisstep is repeated for different positions of the movable stand, thus ofthe test antenna 220.

The test apparatus 210 and measurement system of this disclosure aresubstantially cheaper to construct than creating a curved mirror asrequired in previous systems.

A further aspect of the invention is the placement of the radiatingelements 250-1, 250-2, . . . , 250-N in an angular manner, such as onsidewalls of the measurement apparatus 210.

In a further aspect of the invention the dipoles of the radiatingelements 250-1, 250-2, . . . , 250-N are connected to test the responseof the test antenna 220 in other polarisation directions. This is doneby a Butler matrix for passive antennas and digitally for activeantennas.

It would also be possible to feed test signals of two differentfrequencies to the radiating elements . This will require two differentantenna feed systems 260 or a feed system 260 constructed from activecomponents.

REFERENCE NUMERALS

-   10, 210 Measurement apparatus-   15, 215 Quiet zone-   20, 220 test Antenna-   30 , 230 Measurement stand-   32, 232 Vertical axis-   34, 234 Horizontal axis-   36, 236 Struts-   40, 240 Feed antenna-   245 Wave front-   250-1, 250-2, . . . , 250-N Radiating elements-   260 Antenna feed system-   262 Test signal generator and receiver-   265-1, 265-2, 265-N Delay elements-   265-1, 265-2, 265-N Attenuator elements-   270 Measurement box-   80 Probe-   90 Measurement device

1. A measurement apparatus for the measurement of a test antennacomprising: a movable stand for supporting the test antenna, a feedantenna having a plurality of radiating elements, wherein the movablestand is located at a predefined distance (d) from the feed antenna; andan antenna feed system having a plurality of adjustment components foradjusting the phase and amplitude of a wave front from the plurality ofradiating elements, such that at the distance (d) the wave front issubstantially planar.
 2. The measurement apparatus of claim 1, whereinthe movable stand is rotatable around at least one axis.
 3. Themeasurement apparatus of claim 2, wherein the at least one axis is oneof a vertical axis or a horizontal axis.
 4. The measurement apparatus ofclaim 1, wherein the antenna feed system has at least one of a pluralityof phase element or delay elements connected to the radiating elements,for adjusting the phase of the wave front from the plurality ofradiating elements.
 5. The measurement apparatus of claim 4, wherein adelay distribution set by the plurality of phase element or delayelements is adjusted such that there is substantially no delay at leastin a center portion of the feed antenna.
 6. The measurement apparatus ofclaim 1, wherein the antenna feed system has a plurality of attenuatorsor gain elements connected to the radiating elements, for adjusting theamplitude of the wave front from the plurality of radiating elements. 7.The measurement apparatus of claim 6, wherein a power distribution setby the plurality of attenuators or gain elements is adjusted such that apower is substantially constant at least in a center portion of the feedantenna.
 8. The measurement apparatus of claim 1, wherein the feedantenna comprises between 15 and 30 radiating elements.
 9. Themeasurement apparatus of claim 1, whereby ones of the plurality ofradiating elements comprises at least a pair of radiating elements forproducing two orthogonal polarisation components.
 10. The measurementapparatus of claim 1, whereby the plurality of radiating elements isarranged in a linear array.
 11. A method for the testing of a testantenna in a measurement apparatus comprising: placing the test antennaat a movable stand of the measurement apparatus; adjusting at least oneof a phase, delay and amplitude of a plurality of radiating elementsforming a feed antenna, to produce a substantially planar wave front atthe movable stand, using a plurality of adjustment components foradjusting said at least one of a phase, delay and amplitude; emitting atest signal by a feed antenna and receiving the test signal by the testantenna, to derive a reception pattern of the test antenna.
 12. A methodfor the testing of a test antenna in a measurement apparatus comprising:placing the test antenna at a movable stand of the measurementapparatus; adjusting at least one of phase, delay and amplitude of awave front from a feed antenna comprising a plurality of radiatingelements, to detect a substantially planar wave front at the movablestand, using a plurality of adjustment components for adjusting at leastone of phase or delay; emitting a test signal by the test antenna andreceiving the test signal at the feed antenna to derive a radiationpattern of the test antenna.
 13. The method of claim 12, wherein thetest signal is generated with at least two orthogonal polarisations. 14.The method of claim 12, further comprising rotating the antenna about ahorizontal axis and/or about a vertical axis.
 15. The method of claim12, further comprising setting a same first one of at least one ofphase, delay and amplitude for a first group of radiating elements and asame second one of at least one of phase, delay and amplitude for asecond group of radiating elements.
 16. Use of the measurement apparatusaccording to any claim 1 for testing an active antenna.